Gas turbine electric power plants are utilized in so-called base load, mid-range load and peak load power system applications. Combined cycle plants are normally used for the base or mid-range applications while the power plant which utilizes a single gas turbine as the generator drive is highly useful for peak load applications because of its relatively low cost.
In the operation of gas turbines, particularly in electric power plants, various kinds of control systems have been employed from relay-pneumatic type systems, to analog type electronic controls, to digital controls, and more recently to computer based software controls. U.S. Pat. No. 4,308,463--Giras et al. , assigned to the assignee of the present invention and incorporated herein by reference, lists several of such prior systems. That patent also discloses a digital computer based control system for use with gas turbine electric power plants. It can be said that the control system described in U.S. Pat. No. 4,308,463 is a predecessor to the system described in the present invention. It will be noted that the Giras et al. patent is one of a family of patents all of which are cross referenced therein.
Subsequent to the Giras et al. patent, other control systems have been introduced by Westinghouse Electric Corporation of Pittsburgh, Pennsylvania under the designations POWERLOGIC and POWERLOGIC II. Similar to the Giras et al. patent these control systems are used to control gas turbine electric power plants. However, such control systems are primarily micro-processor based computer systems, i.e. the control systems are implemented in software, whereas prior control systems were implemented in electrical and electronic hardware.
The operating philosophy behind the POWERLOGIC and POWERLOGIC II control system is that it shall be possible for the operator to bring the turbine generator from a so-called ready-start condition to full power by depressing a single button. All modes of turbine-generator operation are to be controlled including control of fuel flow during large step changes in required power output.
The present invention constitutes an improvement to the POWERLOGIC II system. During large step changes in required power output, prior systems would provide a 25 percent rated load maximum for a step change output, which was implemented in an open loop type of control that limited the control signal output (CSO) to the fuel valve. Such an open loop control not only is subject to errors in calibration, but also acts to restrict valve movement during load transients. This restriction on valve movement inhibits fast recovery during transients.
Although, the operation of a gas turbine electric power plant and the POWERLOGIC II control system are described generally herein, it should be noted that the invention is particularly concerned with the control of fuel in the gas turbine and specifically is an improvement to the control of fuel flow during a load transient.